Women will be stratified on the basis of viral load (50,000 or less copies/ml or greater than 50,000 copies/ml) and gestational age at entry (20 or less weeks or greater than 20 weeks) and then randomized to one of two treatment groups. Group A will receive the PI nelfinavir (NFV) with zidovudine (ZDV) and lamivudine (d4T); Group B will receive nevirapine (NVP) with ZDV and d4T. Women will have clinic visits for physical and obstetrical examinations at 2, 4, 6, and 8 weeks after entry and then every 4 weeks until delivery. After delivery, infants in both groups may receive ZDV until they are 6 weeks old. Infants are evaluated for safety and to test the infant's blood for HIV-1 at birth and at Weeks 2, 8, 16, and 24.